Electrolytic water decomposer



from these surfaces into the electrolyte,

United States ELECTROLYTIC WATER DECOFVIPOSER Ewald Arno Zdansky,Monthey, Switzerland, assignor t Lonza Elektrizitiitswerke und ChemischeFabriken A. G., Basel, Switzerland My invention relates to waterelectrolysers, and more particularly to water electrolysers of theso-callcd multicell filter-press type, consisting of a pack ofconsecutively arranged electrolysing cells, each of which being dividedby a diaphragm into an anode chamber and a cathode chamber wherein eachof said cells is enclosed by the adjacent halves of two metal frames,insulated one from another by a packing ring, and wherein each of saidcells is separated from the foregoing and from the following cell byindividual metal partitions, each of which partitions actingsimultaneously as the anode of one cell and as the cathode of thefollowing cell. Said metal partitions, therefore, are usually termed asbipolar main electrodes; as a rule they are associated with perforatedauxiliary electrodes, arranged in a few distance of them on both sidesand conductively connected with them by a plurality of metal bridgepieces.

It is an object of my invention to provide within such electrolyser animproved activating layer on the cathode surfaces, said layer reducingthe voltage consumption of each cell.

A further object of my invention is to prevent such activating layer onthe surfaces of the bipolar main electrodes and to restrict them on thesurfaces of the abovenamed auxiliary electrodes.

A further object of my invention is to prevent a hydrogen production onthe surfaces of the above-named bipolar main electrodes.

Other objects of my invention will appear from the followingdescription, reference having had to the accompanying drawing.

Different methods are known to activate the electrodes of waterelectrolysers by the deposition of chromium, tantalum or sponge iron insuch a manner that a reduction in the so-called overvoltage takes place.Particular importance is attached in this regard to a reduction of theso-called hydrogen overvoltage arising on the cathode surfaces.

Now we have found that surprising advantages can be obtained if suchactivation is restricted to the auxiliary electrodes and in particularto the auxiliary cathodes. This specifically reduces the liberation ofhydrogen at the bipolarly active electrodes which simultaneouslyconstitute the partition between adjacent cells in such a manner thatthese partitions are no longer exposed to embrittlement by theabsorption of hydrogen. This increases their length of life andspecifically in the case of pressure electrolysers leads to a verysubstantial increase in safety; these pressure electrolysers work atseveral atmospheres pressure and consequently demand higher securityagainst cracking and gas penetration. The theoretical disadvantage thatsmaller electrode surfaces are available for the electrolysis has inpractice been found negligible; the bipolar main electrodes are inseries with an electrolytic path of current of greater length than theauxiliary electrodes, so that already for this reason only a relativelysmall current component passes If only the atent 2,871,179 Patented Jan.27, 1959 auxiliary electrodes are activated, this current componentbecomes practically nil, but despite this diminution of the effectivecathode surfaces, the voltage drop across the particular cell decreasesunder otherwise identical loading.

In order completely to suppress any diffusion of hydrogen into theso-called main electrodes (which in the arrangement according to theinvention now act only as partitions) these can be nickel-plated onthecathode side. As the negative overvoltage on a nickeled cathode is about0.2 volt higher than on an iron cathode, it is certain that no currentwill any longer be able to pass from the bipolar main electrodes intothe electrolyte.

The application of an activation layer restricted to the auxiliaryelectrodes is conveniently performed before assembling the cell; mostsuitably for this purpose the perforated sheet or wire mesh fabricconstituting the auxiliary electrode is coated with a noble metal in anappropriate bath. The thus activated auxiliary electrodes can then beattached by spot welding to the contact lugs of the correspondingbipolar main electrode or alternatively placed loosely between thediaphragm and said main electrode; in either case any damage to thesensitive activating coating can easily be prevented.

The invention will now be further described with reference to theaccompanying drawing which shows one embodiment by way of example.

Fig. .1 shows in side elevation part of a cell assembly or'pack. builtup of consecutive disc-shaped individual cells.

Fig. 2 is'a sectional view showing the construction of the individualcells.

As appears from Fig. 1 the assembly of individual cells 1 is held bystrong tierods 2 between an end plate 3 and a second end plate (notshown) of symmetrically identical shape. The cells 1 are traversed atthe top by two consecutively parallel gas collector ducts of which thefront duct 4 is connected by lateral openings with the cathodecompartments K (see Fig. 2) of all cells. This duct or manifold 4 is incommunication through a pipe 5 with a gas separator drum 6 which duringworking of the apparatus is filled with electrolyte up to about thelevel ab.

Electrolyte carried over by the issuing gas into the gas separator 6 isled through a non-return valve 7, a filter 8 and a pump 9 into a duct 10which extends longitudinally through the cell assembly and the two endsof which are connected with pipes 10a and 10b. The gas evolved is drawnfrom the drum 6 (and a further drum for the separation of the oxygenlying concealed behind the drum 6 in Fig. 1) through valves which inknown manner are so controlled or adjusted as to maintain in the cells 1a constant pressure of for instance 25-30 atmospheres.

As shown in Fig. 2 the individual cells are formed by annular frames 11and 12, constituting together annular frame means, in each of which aseparating plate or disc, 13 and 14, is fitted gastight, and which areelectrically insulated from each other by a sealing ring or gasket 15.The disc shaped space of each cell is of a width Z which in practice isrestricted to 8 to 15 millimetres. This is divided by a diaphragm 16into a cathode compartment K and an anode compartment A; for bettercomprehension, both the diaphragm 16a of the preceding cell on the left,and the diaphragm 16b of the next cell on the right have also beenshown. The electrodes are preferably formed of wire mesh fabric 17 and18 applied directly to the diaphragm 16 one on either side and the edgesof which are gripped together with the edge of the diaphragm between theframes 11 and 12; to atford space for this the frames 11 and 12 areprovided with corresponding steps or rebates the radial extension ofwhich corresponds to the depth of the clamping region E within which thediaphragm 16 is dripped between the frames. The sheet metal discs 13, 14acting as dividing partitions between adjacent cells are each providedwith a grid of studs 19, 20 pressed out to projectalternately on eachside of the disc and making contact with the adjacent electrodes of theconsecutive cells. The sheet metal disc 13 thus connects by means of itsstuds 19 the anode 18a of the preceding cell on the left with thecathode 17 of the cell Z representedpsimilarly, the studs 20 on thesheet metal disc 14 connectthe anode 18 of the cell Z represented withthe cathode 17b of the next'following cell.

In accordance with the invention only the auxiliary cathodes 17, 17b areactivated, preferably by the application of a spongy "layer of noblemetal; this is 'indicated-in Fig. 2by the dot-dashed lines P.Furthermore, the so-called bipolar main electrodes '19, 20, which in theactual case are better termed partitions, are coated on both sides, i.e. also on the side towards the cathode compartment K with a dense,firmly adhering plating of nickel. This nickel plating which is suitablyapplied galvanically is indicated in Fig. 2 by the broken lines N. I

What I claim is:

1. In an electrolytic water decomposer, a plurality of series connecteddecomposer cells each of which comprises, in combination, an outerannular frame means defining the outer periphery of said cell; a pair ofspaced electrically conductive separating plates connected at-theirperipheries to said frame means and defining saidcell betweenthemselves, at least one separating plateof each cell also being aseparating plate of an adjacent cell so that such separating plate iscommon to the two cells; a diaphragm connected at its periphery "to saidframe means arating plates; and an activating coating covering only saidanode .and cathode electrodes.

2. In an electrolytic water decomposer, a plurality of series connecteddecomposer cells each of which comprises, in combination, an outerannular frame means defining the outer periphery of said cell; a pair ofspaced electrically conductive separating plates-connected at theirperipheries to saidframe means and defining said cell .betweenthemselves, at least one separating plate of each cell also being aseparating plate of an adjacent cell so that such separating plate iscommon to the two cells; a diaphragm connected at its periphery to saidframe means and located between said separating plates so as to dividesaid cell into anode and cathode chambers; anode and cathode electrodeslocated in said anode and cathode chambers, respectively, adjacent .saiddiaphragm and electrically connected to the respective separatingplates; a nickel coating covering'both faces of each of said separatingplates; and an activating coating covering only said cathode electrode.

References Cited in the file of this patent UNITED STATES PATENTS22,070,612 Niederreither Feb. 16, 1937 OTHER REFERENCES The ChemicalAge, Aug. 19, 1944, pages 173 .to 17.8. The Chemical Age, Aug. 26, 1944,pages 197 to 202.

1. IN A ELECTROLYTIC WATER DECOMPOSER, A PLURALITY OF SERIED CONNECTEDDECOMPOSER CELLS EACH OF WHICH COMPRISES, IN COMBINATION, AN OUTERANNULAR FRAME MEANS DEFINING THE OUTER PERIPHERY OF SAID CELL; A PAIR OFSPACED ELECTRICALLY CONDUCTIVE SEPARATING PLATES CONNECTED AT THEIRPERIPHERIES TO SAID FRAME MEANS AND DEFINING SSID CELL BETWEENTHEMSELVES, AT LEAST ONE SEPARATING PLATE OF EACH CELL ALSO BEING ASEPARATING PLATE OF AN ADJACENT CELLS SO THAT SUCH SEPARATING PLATE ISCOMMON TO THE TWO CELLS; A DIAPHRAGM CONNECTED AT ITS PERIPHERY TO SAIDFROME MEANS AND LOCATED BETWEEN SAID SEPARATING PLATES SO AS TO DIVIDESAID CELL INTO ANODE AND CATHODE CHAMBERS; ANODE AND CATHODE ELECTRODESLOCATED IN SAID ANODE AND CATHODE CHAMBERS, RESPECTIVELY, ADJACENT SAIDDIAPHRAGM AND ELECTRICALLY CONNECTED TO THE RESPECTIVE SEPARATINGPLATES; A NICKEL COATING COVERING BOTH FACES OF EACH OF SAID SEPARATINGPLATES; AND AN ACTIVATING COATING COVERING ONLY SAID ANODE AND CATHODEELECTRODES.